The Air Quality Index (AQI) measures air pollution on a scale from 0 to 500, with higher numbers indicating worse air quality. India uses six categories: Good (0-50), Satisfactory (51-100), Moderate (101-200), Poor (201-300), Very Poor (301-400), and Severe (401-500). Prolonged exposure to poor or worse AQI can cause respiratory issues, especially for vulnerable groups like children, older adults, and those with heart or lung conditions. Even healthy individuals may experience breathing discomfort at severe levels.